Organometallic compounds

ABSTRACT

In a process for the production of thin films and epitaxial layers by gas-phase deposition, intramolecularly stabilized organometallic compounds are employed as a source of metal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/096,583, filed Sep. 15, 1987 now U.S. Pat. No. 4,880,492.

BACKGROUND OF THE INVENTION

The invention relates to the use of organometallic compounds containingaluminum, gallium or indium as metals for the production of thin filmsor epitaxial layers by gas-phase deposition.

The deposition of such layers consisting either of pure elements ofgroup III or of combinations with other elements, such as, for example,gallium arsenide, indium phosphide or gallium phosphide, can be used toproduce electronic and optoelectronic switching elements, compoundsemiconductors and lasers. Such layers are deposited from the gas phase.

The properties of such films depend on the deposition conditions and onthe chemical composition of the deposited film.

All the known methods, such as the metal-organic chemical vapordeposition method (MOCVD), the photo-metal-organic vapor phase method(photo-MOVP) in which the substances are decomposed by UV radiation, thelaser chemical vapor deposition (laser CVD) method or the metal-organicmagnetron sputtering method (MOMS) are suitable for the deposition fromthe gas phase. The advantages over other methods are a controllablelayer growth, a precise doping control, and also simple handling andease of production owing to the normal or low-pressure conditions.

In the MOCVD method, organometallic compounds are used which decomposeat a temperature below 1100° C. with the deposition of the metal.Typical pieces of equipment which are at present used for MOCVD consistof a "bubbler" with a feed for the organometallic components, a reactionchamber which contains the substrate to be coated, and also a source fora carrier gas which should be inert with respect to the organometalliccomponent. The "bubbler" is kept at a constant, relatively lowtemperature which is preferably above the melting point of theorganometallic compound but far below the decomposition temperature. Thereaction or decomposition chamber preferably has a very much highertemperature, which is below 1100° C., at which the organometalliccompound completely decomposes and the metal is deposited. Theorganometallic compound is converted to the vapor state by the carriergas and is channelled into the decomposition chamber with the carriergas. The mass flowrate of the vapor can readily be controlled and,consequently, a controlled growth of the thin layers is also possible.

Hitherto metal alkyls such as, for example, trimethylgallium,trimethylaluminum or trimethylindium have chiefly been used forgas-phase deposition. However, these compounds are extremely sensitiveto air, spontaneously inflammable and, in some cases, unstable even atroom temperature. Costly precautionary measures are therefore necessaryfor the production, transport, storage and use of said compounds. A few,somewhat more stable adducts of the metal alkyls with lewis bases, suchas, for example, trimethylamine and triphenylphosphine, are known (forexample, described in GB 2,123,422, EP-A-108,469 or EP-A-176,537), butthese are only of limited suitability for gas-phase deposition becauseof the low vapor pressure.

SUMMARY OF THE INVENTION

An object of the present invention is to provide metal alkyl compoundswhich are simple to handle, are stable at room temperature and can bedecomposed from the gas phase, i.e. are suitable for the various methodsof gas-phase deposition.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

It has now been found that organometallic compounds of aluminum, galliumand indium which are intramolecularly stabilized are outstandinglysuitable for gas-phase deposition.

Intramolecularly stabilized compounds of this type containing aluminumas metal atom are described, for example, in U.S. Pat. No. 3,154,528,specifically for use as catalyst systems in polymerization reactions.Furthermore, in Organometallics 1982, i, 1492-1495, an indiumderivative, 2-(dimethylaminomethyl)phenyldimethylindium, is describedwhich was used for structural investigations by means of nuclearresonance spectroscopy.

The objects of the invention have therefore been achieved by the use oforganometallic compounds of formula I ##STR1## wherein M denotesaluminum, indium, or gallium,

X denotes --(CHR⁵)_(n) --where n=2, 3, 4 or 5, --2--C₆ H₄ --(CH₂)_(m)--, --(CH₂)_(m) --2--C₆ H₄ --, --2--C₆ H₁₀ --(CH₂)_(m) --, --(CH₂)_(m)--2--C₆ H₁₀ -- where m=1 or 2,

R⁵ in each case denotes H or an alkyl group containing 1-4 carbon atoms,

Y denotes a 5- or 6-membered heterocyclic ring, the heteroatom(s)originating from group 5A, or --NR³ R⁴, --PR³ R⁴, --AsR³ R⁴, or --SbR³R⁴, and

R¹, R², R³ and R⁴ in each case denote, independently of each other, H, astraight-chain or branched alkyl group containing 1-8 carbon atoms,which may be partially or completely fluorinated, a cycloalkyl, alkenylor cycloalkenyl group containing in each case 3-8 carbon atoms or anunsubstituted or substituted phenyl group,

for gas-phase deposition and also a method for producing thin films orepitaxial layers by gas-phase deposition of the metal fromorganometallic compounds in which the compounds of the formula I areused as organometallic compounds. Furthermore, a subject of theinvention is that, in the novel method for preparing compoundedsemiconductors, one or more compounds of arsenic, antimony or phosphoruswhich are gaseous under the reaction conditions employed, are suppliedduring the deposition process.

In formula I M preferably denotes indium or gallium. Preferably, Xdenotes --(CHR⁵)_(n) -- where n is equal to 2, 3, 4, or 5, n preferablybeing equal to 3 or 4. R⁵ represents either an H atom or a methyl,ethyl, propyl or butyl group. R⁵ is preferably H. If R⁵ is an alkylgroup, then preferably only one R⁵ in --(CHR⁵)_(n) -- is alkyl, theothers then denoting H.

Furthermore, X may denote a --2--C₆ H₄ --(CH₂)_(m) -- or a --2--C₆ H₁₀--(CH₂)_(m) -- group, and furthermore also a --(CH₂)_(m) --2--C₆ H₄ --or --(CH₂)_(m) --2--C₆ H₁₀ -- group. In this case m is preferably 1.

Y in formula I denotes preferably --NR³ R⁴, but also --PR³ R⁴, --AsR³ R⁴or --SbR³ R⁴. Y may also be a 5- or 6-membered heterocyclic ring(aromatic, or saturated or unsaturated aliphatic) containing one or more(e.g., 1, 2 or 3) atoms of group 5A, such as N, P or As. In particular,the following rings (1) to (5) are preferred: ##STR2## R⁶ denoting H oran alkyl radical containing 1-8 carbon atoms.

The radicals R¹, R², R³ and R⁴ in formula I may in each case denote astraight-chain or branched alkyl group containing 1-8 carbon atoms,preferably containing 1-4 carbon atoms. They consequently denotepreferably methyl, ethyl, propyl, butyl, isopropyl, sec-butyl,tert-butyl, but also pentyl, hexyl, heptyl, octyl, 2-methylpentyl,3-methylpentyl or 2-octyl. The alkyl radicals may be partially or evencompletely fluorinated and may denote, for example, monofluoromethyl,trifluoromethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl ortrifluoropropyl.

If R¹, R², R³ and/or R⁴ denote a cycloalkyl or cycloalkenyl group, thenthey preferably represent cyclopentyl, cyclohexyl or cyclohexenyl. R¹ toR⁴ may also be alkenyl groups containing 3-8 carbon atoms, i.e.propenyl, butenyl, pentenyl, hexenyl, heptenyl or allyl. If R¹ and/or R²and/or R³ and/or R⁴ denote(s) a phenyl group then the latter ispreferably unsubstituted, but it may also be substituted. Since thesesubstituents exert no substantial influence on the desired application,all substituents are permitted which have no disturbing influence on thedecomposition reaction.

The following compounds may be regarded as exemplary representatives ofcompounds of formula I:

(2-dimethylaminobenzyl)dimethylindium

(3-dimethylaminopropyl)dimethylaluminum

(3-diethylaminopropyl)dimethylaluminum

(3-diethylaminopropyl)diisobutylaluminum

(3-diisopropylaminopropyl)dihexylaluminum

(4-N-methyl-N-isopropylaminobutyl)diethylaluminum

[3-(1-piperidyl)propyl]diethylaluminum

[2-(2-pyridyl)ethyl]dimethylaluminum

[3-(2-pyridyl)propyl]diisobutylaluminum.

The intramolecular stabilization, which is based on a bond between themetal atom and the particular heteroatom of group Y, which is separatedfrom the metal by 2, 3, 4 or 5 carbon atoms, is essential for the noveluse of the compounds of formula I. As a result of this intramolecularbond, the compounds of the formula I attain a significantly higherstability towards air and oxygen compared with the free metal alkyls.They are no longer spontaneously inflammable and can therefore behandled simply and without fairly considerable precautionary measures.

Some of the compounds of Formula I are known, but most are novel.

New compounds are, in particular, those of formula II ##STR3## wherein Mdenotes aluminum, indium or gallium,

X' denotes --2--C₆ H₄ --(CH₂)_(m) --, --(CH₂)_(m) --2--C₆ H₄ --, --2--C₆H₁₀ --(CH₂)_(m) --, --(CH₂)_(m) --2--C₆ H₁₀ --, where m=1 or 2,

Y' denotes --NR³ R⁴, --PR³ R⁴, --AsR³ R⁴ or --SbR³ R⁴ and

R¹, R², in each case denote, independently of each other,

R³, R⁴ H, a straight-chain or branched alkyl group containing 1-8 carbonatoms, which may be partially or completely fluorinated, a cycloalkyl,alkenyl or cycloalkenyl group containing in each case 3-8 carbon atomsor an unsubstituted or substituted phenyl group,

with the proviso that R¹, R², R³ and R⁴ do not simultaneously denotemethyl if M denotes indium, X' denotes --2--C₆ H₄ --CH₂ -- and Y'denotes --NR³ R⁴.

At the same time, M preferably denotes gallium or indium. X' ispreferably --2--C₆ H₄ --CH₂ --, --CH₂ --2--C₆ H₄ -- or --2--C₆ H₁₀ --CH₂--. Y' preferably has the meaning of NR³ R⁴. R¹, R², R³ and R⁴ have andmeanings specified for formula I.

The compounds of the formula II include, for example, the followingsubstances:

2-dimethylaminobenzyl (dimethyl)gallium

2-dimethylaminobenzyl (dimethyl)aluminum

2-diethylaminobenzyl(dimethyl)indium

2-dimethylaminobenzyl(diethyl)indium

2-diethylaminobenzyl(diethyl)gallium

2-diethylaminobenzyl(dimethyl)gallium

2-dimethylaminophenylmethyl(dimethyl)gallium

2-dimethylaminophenylmethyl(dimethyl)indium

2-dimethylaminophenylmethyl(dimethyl)gallium

2-dimethylaminophenylmethyl(dimethyl)aluminum

2-diethylaminocyclohexylmethyl(dimethyl)gallium

2-dipropylaminocyclohexylmethyl(dimethyl)aluminum

2-dimethylaminomethylcyclohexyl(dimethyl)indium.

The compounds of formula III are also new: ##STR4## wherein M' denotesgallium or indium,

X" denotes --(CHR⁵)_(n) -- where n=2, 3, 4, or 5,

R⁵ in each case denotes H or an alkyl group containing 1-4 carbon atoms,

Y" denotes 5- or 6-membered heterocyclic ring, the heteroatom(s)originating from group 5A or --NR³ R⁴, --PR³ R⁴, AsR³ R⁴ or --SbR³ R⁴,and

R¹, R², in each case denote, independently of each

R³, R⁴ other, H, a straight-chain or branched alkyl group containing 1-8carbon atoms which may be partially or completely fluorinated, acycloalkyl, alkenyl or cycloalkenyl group containing in each case 3-8carbon atoms or an unsubstituted or substituted phenyl group.

At the same time, n in X" preferably denotes 3 or 4. Y" is preferably--NR³ R⁴, but also --PR³ R⁴ or --AsR³ R⁴. If Y" is a heterocycliccompound containing atom(s) of group 5A, then rings containing N, P orAs, but preferably the rings (1) to (5) specified for Y in formula I,are suitable. The meanings specified for formula I apply to R¹ -R⁴.

A number of compounds are listed below as exemplary representatives:

(3-dimethylaminopropyl)dimethylgallium

(3-dimethylaminopropyl)dimethylindium

(3-diethylaminopropyl)dimethylgallium

(3-diethylaminopropyl)dimethylindium

(3-diethylaminopropyl)diethylindium

(4-diethylaminobutyl)dimethylgallium

(4-diisopropylaminobutyl)dimethylindium

[2-(2-pyridyl)ethyl]dimethylindium

(4-N-methyl-N-isopropylaminobutyl)diethylgallium

(4-dimethylaminobutyl)diisopropylgallium

(3-dipropylaminopropyl)diethylgallium

(3-N-propyl-N-isopropylaminopropyl)diisobutylindium

(4-dimethylaminobutyl)diethylindium

(4-diethylaminobutyl)diethylgallium.

The compounds of the formulae I, II and III are outstandingly suitablefor MOCVD epitaxy or for the MOCVD method since they decompose at fairlyhigh temperatures to liberate the relevant metal. The are likewisesuitable for the other methods of gas-phase deposition, such asphoto-MOVP, laser CVD or MOMS.

The compounds of formulae I, II and III are prepared by methods whichare known per se such as are described in the literature (for example,G. Bahr, P. Burba, Methoden der Organischen Chemie (Methods of OrganicChemistry), volume XIII/4, Georg Thieme Verlag, Stuttgart (1970)),specifically under reaction conditions which are known and are suitablefor the reactions mentioned. At the same time, use may also be made ofvariants which are known per se but not mentioned here.

Those skilled in the art may obtain suitable methods of synthesis byroutine methods from the prior art (for example, U.S. Pat. No.3,154,528, or Jastrzebski et al, Organometallics 1982, 1, 1492, orMuller, Chem. Ber. 88, 251, 1765 (1955)).

Thus, compounds of the formulae I, II and III may be prepared, forexample, by reacting metalalkyl chlorides with an alkali metal organiccompound of the corresponding Lewis base or a Grignard compound in aninert solvent.

The reactions are preferably carried out in an inert solvent. Suitablesolvents in this connection are all those which do not interfere withthe reaction and do not intervene in the reaction process. The reactiontemperatures essentially correspond to those which are known from theliterature for the preparation of similar compounds.

In the novel method for the production of thin films or epitaxial layerson any desired substrate, use is made of the intramolecularly stabilizedcompounds of the formulae I, II and III as starting organometalliccompounds in the gas-phase deposition processes known per se oforganometallic compounds.

To produce compound semiconductors, one or more compounds of arsenic,antimony or phosphorus which are gaseous under the reaction conditionsused are added during the deposition process in the decompositionchamber.

The layers produced by the novel methods may be used for the productionof electronic and optoelectronic switching elements, compoundsemiconductors or lasers.

The deposition methods of this invention are fully conventional exceptfor the use of the compounds of formula I and the concomitantadvantages. For the conventional aspects, see, e.g. M. J. Ludowise in J.Appl. Phys. 58 (8), 1985, 31 or J. B. Webb in Appl. Phys. Lett. 47 (8),1985, 831.

Typically, for this invention, decomposition temperatures will be400°-1000° C.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description; utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the following examples, all temperatures are setforth uncorrected in degrees Celsius and unless otherwise indicated, allparts and percentages are by weight.

The entire text of all applications, patents and publications, if any,cited above and below are hereby incorporated by reference.

In the following examples, M.p. denotes melting point and B.p. denotesboiling point.

EXAMPLES Example 1

12 g (89 mmol) of dimethylgallium chloride are made ready for use in 300ml of pentane and cooled to -78°. 8.3 g (89 mmol) ofdimethylaminopropyllithium are added thereto as a solid. The solution isallowed to come to room temperature and is stirred for a further 24hours. The lithium chloride precipitated is separated off, the solventis removed and the residue is distilled in vacuo.Dimethylaminopropyl(dimethyl)gallium is obtained as a white solid with aB.p. of 65°/10 mbar.

Example 2

3.6 g (30 mmol) of diethylaminopropyllithium dissolved in 100 ml ofpentane are added to a solution of 4 g (30 mmol) of dimethylgalliumchloride in 50 ml of pentane at -78°. The solution is allowed to come toroom temperature and is stirred for a further 24 hours. The working upis carried out analogously to Example 1. Instead of the distillation, asublimitation is carried out. Diethylaminopropyl(dimethyl)gallium withan M.p. of 43°-45° is obtained.

Example 3

4.3 g (30 mmol) of o-lithium-N,N-dimethylbenzylamine are added to asolution of 4 g (30 mmol) of dimethylgallium chloride in 150 ml ofpentane at -78°. Working up is carried out analogously to Example 1 withsublimitation as the purification step.1,2-Dimethylaminobenzyl(dimethyl)gallium with an M.p. of 29°-31° isobtained.

Example 4

Dimethylaminopropyl(dimethyl)aluminum with M.p. of 52° is obtainedanalogously to Example 1 from dimethylaluminium chloride anddimethylaminopropyllithium.

Preparation Example 5

5.47 g (30 mmol) of (3-dimethylarsinopropyl)chloride are added to 1.44 g(60 mmol) of magnesium chips in 100 ml of diethylether at 20° C., andthen the mixture is heated under reflux for two hours. The solution isallowed to come to room temperature, 4.0 g (30 mmol) of dimethylgalliumchloride in 50 ml of diethylether are added, and the solution isrefluxed again for two hours. The working up is carried out analogouslyto Example 1. (3-Dimethylarsinopropyl)-dimethylgallium is obtained as aclear liquid with a B. p. of 86° C./0.01 mbar.

Preparation Example 6

Analogously to Example 3, 1,2-diethylphosphinobenzyl(dimethyl)indiumwith a B. p. of 88° C./0.3 mbar is obtained by reactingo-lithium-diethylbenzylphosphine with dimethylindium chloride. Theworking up is carried out analogously to Example 1.

B. Use for Producing Thin Films Example 1

Dimethylaminopropyl(dimethyl)gallium (prepared according to Example 1)is filled into the "bubbler" and connected to the gas supply of theinert gas and the decomposition chamber. Depending on the partial vaporpressure of the reagent in the reactor, decomposition takes places withthe deposition of gallium at temperatures from approximately 700° C.

Example 2

Diethylaminopropyl(dimethyl)indium (which can be prepared analogously toExample 1) is filled into the "bubbler", converted to the vapor state bymeans of the carrier gas, and conveyed to the decomposition chamber. Aphosphine is additionally passed into the decomposition chamber. Thegaseous substances decompose in the decomposition chamber at atemperature of approximately 650° and deposit on the substrate as an InPcoating.

Example 3

1,2-Diethylphosphinobenzyl(dimethyl)indium was decomposed with PH₃ in aMOCVD apparatus under normal pressure. The growth temperature rangedbetween 580° C. and 660° C.; an epitaxial InP-layer was obtained.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. In a process for gas-phase deposition of a metalcompound containing Al, In or Ga on a substrate, the improvement whereina source of Al, In or Ga for the deposition process is an organometalliccompound of the formula ##STR5## wherein M is Al, In or Ga;X is--(CHR⁵)_(n) -- where n=2, 3, 4 or 5, --2--C₆ H₄ --(CH₂)_(m) --,--(CH₂)_(m) --, --(CH₂)_(m) --2--C₆ H₄ --, --2--C₆ H₁₀ --(CH₂)_(m) --,or --(CH₂)_(m) --2--C₆ H₁₀ -- where m=1 or 2; R⁵ is H or alkylcontaining 1-4 carbon atoms; Y is --PR³ R⁴, --AsR³ R⁴, SbR³ R⁴, or a 5-or 6-membered heterocyclic ring where the heteroatoms are from group 5A;and R¹, R², R³ and R⁴ are each independently H, straight-chain orbranched alkyl containing 1-8 carbon atoms, partially or completelyfluorinated straight-chain or branched alkyl containing 1-8 carbonatoms, cycloalkyl, alkenyl or cycloalkenyl containing in each case 3-8carbon atoms, unsubstituted phenyl or substituted phenyl.
 2. A processaccording to claim 1, wherein an epitaxial layer is deposited.
 3. Aprocess according to claim 1, wherein a thin film is deposited.
 4. Aprocess according to claim 1, wherein X is --(CHR⁵)_(n) -- and n is 3 or4.
 5. A process according to claim 1, wherein X is --(CHR⁵)_(n) --, oneR⁵ group is alkyl, and the remaining R⁵ groups are H.
 6. A processaccording to claim 1, wherein X is --2--C₆ H₄ --CH₂ --, --2--C₆ H₁₀--CH₂ --, --CH₂ --2--C₆ H₄ --, or --CH₂ --2--C₆ H₁₀.
 7. A processaccording to claim 1, wherein R¹ to R⁴ are each independentlystraight-chain or branched alkyl containing 1-4 carbon atoms, partiallyor completely fluorinated straight-chain or branched alkyl containing1-4 carbon atoms, propenyl, butenyl, pentenyl, hexenyl, heptenyl, allyl,cyclopentyl, cyclohexyl, cyclohexenyl, or unsubstituted phenyl.